High Availability and Scalability with ALB and Auto Scaling

SAA-C03 By islever Editorial Last updated

Design scalable and loosely coupled architectures. Design highly available and/or fault-tolerant architectures.

Short answer

BE Configure an Application Load Balancer to distribute traffic and EC2 Auto Scaling with multiple Availability Zones to handle demand.

Question

A company's web application that is hosted in the AWS Cloud recently increased in popularity. The web application currently exists on a single Amazon EC2 instance in a single public subnet. The web application has not been able to meet the demand of the increased web traffic. The company needs a solution that will provide high availability and scalability to meet the increased user demand without rewriting the web application. Which combination of steps will meet these requirements? (Choose two.)
  1. Replace the EC2 instance with a larger compute optimized instance.
  2. Configure Amazon EC2 Auto Scaling with multiple Availability Zones in private subnets. Correct Answer
  3. Configure a NAT gateway in a public subnet to handle web requests.
  4. Replace the EC2 instance with a larger memory optimized instance.
  5. Configure an Application Load Balancer in a public subnet to distribute web traffic. Correct Answer

Key Takeaways

The exam tests the architectural pattern of decoupling compute from traffic using ALB and Auto Scaling, while avoiding the trap of scaling vertically or misusing NAT gateways.

This question addresses how to achieve high availability and scalability for a web application on AWS without code changes. The correct solution combines an Application Load Balancer for traffic distribution and Auto Scaling for dynamic capacity management.

Common mistake: Candidates often choose vertical scaling (larger instances) because it is simpler, but this does not provide high availability or true scalability against traffic spikes.

Expert Analysis

Why the Answer Is Correct

To meet requirements for high availability and scalability without rewriting the application, you must implement a distributed architecture. Option E, configuring an Application Load Balancer (ALB) in a public subnet, distributes incoming web traffic across multiple targets, providing a single point of entry and health checking. Option B, configuring Amazon EC2 Auto Scaling with multiple Availability Zones (AZs), ensures that the system can automatically add or remove EC2 instances based on demand and maintains service even if one AZ fails. This combination directly addresses both scalability (handling increased demand) and high availability (redundancy across AZs).

Why the Other Options Are Wrong

Option A and D suggest replacing the instance with a larger type (vertical scaling). While this might temporarily handle more load, it does not provide high availability (a single point of failure remains) and has a hard limit on scalability. It also violates the spirit of cloud-native scalability which favors horizontal scaling. Option C suggests using a NAT gateway to handle web requests. This is incorrect because NAT gateways are used for outbound internet access for resources in private subnets, not for distributing inbound web traffic.

Community Comment Notes

The community consensus strongly supports options B and E. Comments highlight that Auto Scaling increases server count per need and the Load Balancer balances traffic equally. One user questioned why a NAT gateway wasn't the answer, likely confusing inbound and outbound traffic flows. Another noted that while modifications might be needed, this is the standard architectural approach for this scenario.

Exam Strategy

Always look for 'High Availability' and 'Scalability' keywords together; this almost always points to multi-AZ deployments combined with Load Balancers and Auto Scaling groups. Avoid vertical scaling options unless the question explicitly states hardware limitations prevent horizontal scaling.

Frequently Asked Questions

Why isn't a NAT Gateway used for web traffic?

NAT Gateways handle outbound traffic from private subnets. Inbound web traffic requires a Load Balancer or Public Subnet.

Does changing instance size help with high availability?

No, vertical scaling (larger instances) does not eliminate single points of failure. You need redundancy across multiple instances/AZs.

More SAA-C03 FAQ →

Community Votes

BE
100%

100% of anonymous learners picked answer BE. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 6 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 6

  1. sandordini 👍 4
    Only BE makes sense, even though it might require modification of the application
  2. Scheldon 👍 2
    AnswerBE, AutoScaling to increase amount of servers per need, Load Balancer to palance traffic equaly to all available servers
  3. kempes 👍 6
    Option BE
  4. chefKC 👍 3
    Option B & E
  5. asdfcdsxdfc 👍 2
    be are correct
Show 1 more comment
  1. gsgdga 👍 1
    Why isn't C the answer?

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